Wide-bodied commercial jet aircraft are potentially subject to critical damage to the passenger compartment floor as a result of a large hole made in a lower cargo compartment, such as a hole formed by the sudden opening of a cargo door or a small bomb explosion, while the airplane cabin and cargo compartments are at a high pressure differential with respect to the outside atmospheric air pressure. Upon rapid decompression of the lower cargo compartment, severe downloads may be placed on the passenger floor due to the air pressure above the floor. The air above the floor cannot escape rapidly into the cargo compartment and eventually to atmosphere, as the passenger compartment floor is normally made as a sealed floor due to air conditioning requirements, noise requirements, liquid spillage prevention requirements and appearance considerations. Consequently, because of this pressure differential, structural damage to the floor and nearby components, controls, and systems may occur, with the safety of the aircraft potentially placed in jeopardy.
A relatively new Federal Aviation Administration rule has required that airframe manufacturers either strengthen the floor structure to withstand the sudden differential pressure load, or increase the venting capacity between the upper and lower compartments in order to reduce the maximum differential pressure to a level which the existing floor could withstand.
Since strengthening of the floor structure would require significant weight increase, which would adversely affect aircraft performance, a decompression vent box was developed to increase the venting capacity between upper and lower compartments. This vent box is described below with reference to FIGS. 1 and 2.
The decompression vent box 10, shown in FIGS. 1 and 2, is provided for allowing air flow through the floor support opening 12 in the event of decompression. The vent box 10 comprises a collapsible diaphragm 14 hinged between a baffle 16 and face panel 18. A spring 20 holds the vent box 10 in the closed position, as shown in FIG. 1, until a negative pressure differential force acting against the hinged diaphragm 14 pivots the face panel 18 and collapses the hinged diaphragm 14, as shown in FIG. 2, to allow air flow through the floor support opening 12. Accordingly, in the event of a sudden opening of a large hole in the lower cargo compartment, the diaphragm will collapse and expose the floor support opening 12, which is large enough to handle increased venting to reduce the differential pressure to a level which the existing floor could withstand. Also, in the case of sudden decompression in the upper compartment due to loss of cabin door or holes in the upper fuselage skin due to fan blade penetration as the result of an uncontained engine failure, the hinged flapper 17 in the face panel 18 swings open to allow increased airflow to increase venting and reduce the differential pressure to a level which the floor can withstand.
Under normal operation, small holes formed in the hinged flapper 17 act as a flow-controlling orifice to allow limited air movement therethrough.
Some problems with this vent box design are that it may add approximately 450 pounds of weight to the aircraft, its reliability has been questioned, and it has been known to leak uncontrollably.
Accordingly, it is desirable to provide a frangible aircraft floor with reduced weight and improved reliability.